From: "adrianomitre (Adriano Mitre)" <adriano.mitre@...>
Date: 2012-08-28T17:52:08+09:00
Subject: [ruby-core:47342] [ruby-trunk - Bug #6944][Open] BigDecimal#to_f breaks for numbers too small to be representable in Float


Issue #6944 has been reported by adrianomitre (Adriano Mitre).

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Bug #6944: BigDecimal#to_f breaks for numbers too small to be representable in Float
https://bugs.ruby-lang.org/issues/6944

Author: adrianomitre (Adriano Mitre)
Status: Open
Priority: High
Assignee: 
Category: lib
Target version: 1.9.2
ruby -v: ruby 1.9.2p290 (2011-07-09 revision 32553) [x86_64-linux]


BigDecimal numbers too small to be representable in Float are incorrectly converted to +/-Infinity instead of 0.0 (or -0.0). Things seem to broke down when exponent is about -308.

# with 307, ok
BigDecimal('1e-307').to_f
# => 1.0e-307
BigDecimal('-1e-307').to_f
# => -1.0e-307

# with 308, broken but signedness is correct
BigDecimal('1e-308').to_f
# => Infinity
BigDecimal('-1e-308').to_f
# => -Infinity

# with 350 not even signedness is correct
BigDecimal('1e-350').to_f
# => -Infinity
BigDecimal('-1e-350').to_f
# => -Infinity

# Workaround: resort to BigDecimal#to_s and Float(.)
x=BigDecimal('1e-350')
Float(x.to_s)


-- 
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